The invention relates to a method and an apparatus for controlling the operation of an internal combustion engine during and after engine braking, thereby improving driver comfort and diminishing the concentration of toxic exhaust components. The invention relates more particularly to a method and apparatus for changing the engine timing in a manner related to the occurrence of engine braking.
During engine braking or overrunning, there exists a state of operation in which the engine delivers no torque to the vehicle but is turned at a speed higher than that which would result from a given load condition and a given throttle position due to the momentum of the vehicle in which it is installed. In such a state of operation, the accelerator pedal would normally be permitted to assume its zero position. In particular, if the accelerator pedal is released while the vehicle is in normal operation, the engine will enter a condition of engine braking. This condition may be accompanied, as is usually the case, by actuation of the wheel brakes but is may also occur, for example, in downhill operation, without application of the wheel brakes.
The engine braking which takes place under these conditions is normally desired. However, to insure the most effective degree of engine braking, the engine must be prevented from delivering a positive torque, i.e., the combustion processes must either be suppressed or must be conducted with such timing as would prevent the delivery of positive torque. Generally, the fuel supply is entirely interrupted which results in fuel economy and is referred to as fuel cut-off or engine braking cut-off. In order to insure that the engine will operate properly at idling speed, however, the fuel supply is restored when the engine speed has dropped to a so-called reinstatement speed hereinafter labeled "nW." Fuel cut-off during engine braking may take place, in principle, in all fuel injection systems and even in engines having carburetors with the aid of solenoid valves associated with the idling mechanism of the engine. Fuel cut-off has the advantage of providing fully effective engine braking and a substantial saving in fuel, especially when the vehicle is operated in heavy traffic.
The invention constitutes an improvement of a fuel supply system for an internal combustion engine in which the fuel supply is shut off during engine braking until a reinstatement speed nW has been reached. Subsequently, the combustion chambers of the engine again receive fuel. It has been shown in practice that, when the fuel supply is reinitiated, the vehicle is subjected to a certain forward lurch or jolt which leads to driver discomfort. In addition, the emission of toxic substances is increased for some time, after the reinitiation of fuel supply because the engine generally is cooled off substantially during engine braking and the formation of a satisfactory optimum mixture is difficult, thereby preventing full combustion.